It is proposed to investigate several new film/screen combinations with the potential for greater sensitivity to low-energy x rays used in mammography. The first new system will utilize yttrium oxysulfide (Tb) which offers significant speed gains over existing mammographic systems such as xeroradiography and the duPont Lo-Dose system because of the efficient light production in this material. The properties of new rare-earth activated screen materials and the possibility of direct compact deposition by evaporation or sputtering in vacuo will be investigated. Physical measurements of resolution, speed and contrast, noise level and necessary skin dose for mammography will be made for both tungsten and molybdenum anode x-ray tubes. Subsequently clinical trials in comparison with existing x-ray screening methods will be performed using the optimal low dose system.